Abstract
Calcined marl – ordinary "blue" clay containing calcium carbonate – has been shown earlier to be an effective pozzolan in cementitious materials in terms of strength if calcined at the
correct temperature. Marl is unsuitable for the clay product industry, and might thus be the high-volume available alternative pozzolan globally that the cement and concrete industry is
looking for in order to reduce their carbon footprint.
The objective of the present study was to investigate how durability of mortars is affected when calcined marl is replacing cement by volume at levels of 0, 20, 35, 50 and 65vol%.
Excellent strength at both 1 and 28 days relative to reference is obtained when up to 50 vol% is replaced by calcined marl, and the strength continues to increase up to 1 year (last
measuring point). The capillary porosity volume is increasing, but the electrical resistivity is also increasing, indicating a pore refinement or segmentation, as well as perhaps reduced
ionic strength in the pore water. These are properties that might reduce the propagation rate of rebar corrosion once initiated by carbonation. Furthermore, the chloride ingress is
significantly reduced when cement is replaced by calcined marl.
The carbonation rate is increasing with increased cement replacement by calcined marl, but this effect may be counteracted by reducing the water-to-cement ratio (w/c) further. Just note that if w/c is reduced the conventional way by increasing the cementitious binder to aggregate ratio, the effect on reduced CO2 emission may be considerably reduced due to the
higher volume of binder per cubic meter of concrete. Hence, lean concrete mixes should be made with the aid of appropriate plasticizing admixtures.